1. Field of the Invention
The present invention generally relates to an interposer for a chip package. More particularly, the present invention relates to a high performance interposer for a chip package using deformable button contacts that enables broadband high speed I/O.
2. Description of the Related Art
High pin count chip packages have evolved away from pins because of the requirement for through holes that prevent a high density from being achieved and because the pins do not permit for easy replacement of a chip in the field.
A relatively new type of technology allows one to mount a ceramic or organic chip package onto a printed circuit board (PCB) without soldering by using, for example, button contacts.
This technology uses a regular array of button contacts (hereinafter referred to as “buttons”) that may be made from a compressible material, such as an elastomer or other rubber-like compound, in which are embedded a very high density of metallic particles such as, for example, silver and the like. Then, when these buttons are compressed in a chip package between a chip and a printed circuit board, the silver particles contact each other and form a very low resistance conductor.
This array of compressible buttons is typically sandwiched between a printed circuit board and a chip carrier that each have contact pads that align with and compress the buttons between them. The chip carrier maintains compression on the array of compressible buttons to establish contacts between the chip and the printed circuit board using, for example, a clamping ring around the perimeter of the package.
Typically, the compressible buttons are formed, for example, on a sheet or membrane.
FIG. 1 shows a cross-sectional view of a conventional interposer 100 having compressible buttons 102 formed on a thin carrier membrane 104. FIG. 2 shows a magnified view of one of the compressible buttons 102 on the membrane 104. FIG. 3 illustrates one of the compressible buttons 102 being compressed between a chip carrier 302 and a printed circuit board 304.
Since the compressible buttons may be relatively pliable, any mismatch between thermal coefficients of expansion between the chip carrier 302, the interposer 100 and the printed circuit board 304, that may cause a differential strain between these elements, will be readily accepted by the buttons without loss of continuity of the contacts and/or causing structural failure.
Therefore, this conventional technology provides a method and system for providing demountable chips with high I/O counts while still providing good reliability in terms of accommodating thermal expansion mismatch, and the like.